Humans Brought Domesticated Dogs to New World More Than 12,000 Years Ago, UCLA Biologists, Colleagues Report
When the first Americans arrived in the New World at least 12,000 years ago, these hunter-gatherers brought domesticated dogs with them, UCLA evolutionary biologists and colleagues reported in the Nov. 22 issue of the journal Science.
The international team of scientists used molecular genetic techniques to analyze mitochondrial DNA from ancient bones of dogs from archaeological sites across Latin America and Alaska pre-dating Columbus' journey to America.
A former graduate student in the lab of UCLA biology professor Robert K. Wayne, Jennifer A. Leonard — currently a postdoctoral fellow at the Smithsonian Institution's National Museum of Natural History — extracted DNA from bones of dogs from archaeological sites in Peru, Bolivia and Mexico, and compared the DNA with DNA from modern dogs and modern wolves. Much of the DNA was well preserved, Leonard said.
The hunter-gatherers brought the dogs enormous distances, which shows that the dogs were regarded as very valuable.
"Dogs are expensive traveling companions, who require food and care," said Wayne, a co-author of the research. "They must have served an important function in ancient societies, and have been thoroughly domesticated to move great distances without wandering off into the countryside. We believe they were a fundamental part of ancient societies. Dogs may have been valued for their hunting skills, security, transport, warmth, perhaps even helping early travelers to move great distances.
"Dogs are the only domesticated animal that had a New World and Old World distribution before the arrival of Columbus to North America," Wayne said.
"Our results show that ancient American dogs were more similar to dogs from the Old World than to gray wolves of North America," Leonard said. "This implies that when nomadic hunter-gatherers migrated across the Bering Strait from Asia into North America, at least
12–14,000 years ago, they already had dogs with them. The diversity observed in the ancient American dogs indicates that multiple lineages of dogs were taken in to the New World."
What characteristics of dogs caused them to have such high value in ancient societies and why were they domesticated thousands of years before other animals and plants? The answers to these questions are obscured by the long unwritten history of dogs and by the dramatic difference between the role of dogs in ancient and modern societies, Wayne said.
"Did dogs contribute to the rapid expansion of humans into the New World?" Wayne asked. "At this point we can only speculate about the way dogs changed early human societies, but our new findings suggest that the effect may have been profound."
When did the association between humans and dogs begin? By the time humans arrived in the New World, the diversity of dogs was already substantial and dogs were spread across Eurasia, Wayne said.
"This suggests a very long coexistence of humans and dogs," Wayne said. "Previous genetic analyses support this conclusion and have suggested that this association could have lasted tens of thousands of years. Dogs have been living in close association with humans much longer than any other domestic animal or plant species."
Although New and Old World dogs are descended from the same Old World wolf ancestor, the DNA sequences from ancient American dogs are slightly different from their modern counterparts.
"Consequently, these data suggest Native American dogs have not genetically contributed to modern dog breeds," Wayne said. "DNA sequences from hundreds of dogs from dozens of modern breeds from throughout the world do not show traces of American ancestry. Native dogs may still have living descendants in some unsampled New World population, but their absence for a large sample of modern dogs reinforces the dramatic impact that the arrival of Europeans had on native cultures."
The new molecular genetic analysis suggests that the majority of the living dog gene pool does not contain any ancestry from these long isolated Native American dogs, Wayne said.
"This implies selective breeding, either intentional — where European colonists forcefully discouraged the breeding of native dogs, as they did with other aspects of native culture — or dogs of European origin may simply have been considered more desirable; both scenarios may have occurred in different regions. There was not wide-scale interbreeding of European and native American dogs; native American breeds did not persist into the modern dog gene pool."
The scientists on the study also include evolutionary biologist Carles Vila from Uppsala University, Sweden, and zooarchaeologists from Mexico and Peru: Jane Wheeler, Raul Valadez and Sonia Guillen.
Wayne's research was partially funded by the National Science Foundation.